1. Field of the Invention
The present invention relates to a process for increasing the retention of fines, fillers and pigments during the manufacture of paper while at the same time decreasing pitch deposition on the paper machine.
2. Description of the Prior Art
In the papermaking process much of the water in the pulp is separated from the fibres, fillers and pigments by filtration. The filtrate, which is called white water, contains a large amount of fines which may be fibre fragments, mineral fillers, or pigment particles. The poor retention of fines is a consequence of the difficulty in the filtration of material characterized by colloidal or nearly colloidal dimensions. Poor fines retention is a serious problem because it results in the loss of valuable material, additional loading of water treatment facilites, and possibly drainage problems on the paper machine. Retention problems in the manufacture of fine papers have been alleviated, in part, by the use of polymeric flocculants which are called retention aids. However, other grades of paper and, in particular, newsprint and groundwood specialties are characterized by poor fines retention and, in most cases, no economic benefit is gained by the use of existing retention aids. However, it is known from the teachings of U.S. Pat. No. 3,141,815 issued in July 21, 1964 to Manley, that poly(oxyethylene) can increase fines retention in certain commercial newsprint pulps. Still further, U.S. Pat. No. 4,070,236 to Carrard et al, issued Jan. 24, 1978, teaches that mixtures of poly(oxyethylene) and certain synthetic phenolic polymers will increase retention in paper making furnish based on mechanical pulp. However, the cost of the compounds involved is believed to be one reason why the process has not been widely commercially acceptable.
A second problem often associated with the manufacture of paper is the deposition of wood resin as pitch deposits on the surfaces of the process equipment. The term wood resin is used almost universally in the pulp and paper industry to denote the materials in wood and wood pulps which are insoluble in water and soluble in neutral organic solvents. Wood resin therefore includes terpenes, fatty and resin acids, esters, and various alcohols, hydrocarbons and neutral compounds associated with these materials. In aqueous wood pulp slurries the resin is present on the surfaces of the fibres (both in thin patches and droplets), inside parenchyma cells, as soluble soaps, and in the form of colloidal droplets dispersed in the process liquid among the fibres. The mechanisms by which this material deposits have been documented and the most troublesome physical form is usually the dispersed resin in newsprint manufacture. In the past, the most common methods for controlling pitch deposition have included the use of alum, dispersants, talc, sequestrants and a number of non-chemical methods.